The present invention relates to an electroless plating apparatus, a semiconductor wafer having bumps, a semiconductor chip having bumps, methods of manufacturing the semiconductor wafer and the semiconductor chip, a semiconductor device, a circuit board, and electronic equipment.
As the degree of integration of a semiconductor integrated circuit is increased and the size of a semiconductor chip is decreased, mounting technology capable of connecting terminals at a minute pitch has been demanded. As examples of mounting technology capable of easily dealing with such a demand, TAB (Tape Automated Bonding) mounting used for a TCP (Tape Carrier Package) and flip-chip mounting used for a CSP (Chip Size Package) can be given.
In the above mounting technology, bumps are generally formed on pads of the semiconductor chip. Au bumps are typically used as the bumps and generally formed by electroplating. A method of forming Au bump electrodes by electroplating is described below.
FIG. 14 is a cross-sectional view showing an Au bump in a conventional semiconductor chip. A pad 502, which is part of an interconnect linked with an inner integrated circuit, is covered with a passivation film 504 excluding the surface of an electrical connection region.
An under-bump metal layer (laminate of a barrier metal layer and an adhesive metal layer) 506 is formed by using a sputtering method. A resist layer 508 for forming bumps is formed by using photolithographic technology so that the electrical connection region of the pad 502 and its peripheral region are exposed. Au is grown by electroplating corresponding to the pattern of the resist layer 508. After removing the resist layer 508, the under-bump metal layer 506 is wet-etched corresponding to the type of the under-bump metal layer 506 using the grown Au as a mask. A bump 510 is formed by subsequent annealing and the like. A cleaning step is appropriately performed during the process. Since bump formation by electroplating is a long process, further reduction and rationalization of the process have been demanded.
To deal with this demand, formation of bumps by electroless plating has been proposed. If the bumps are formed by electroless plating, it is unnecessary to perform at least the step of forming the under-bump metal layer by sputtering and the step of etching. Moreover, it is expected that formation of a resist for growth of plating can be omitted. This enables the process to be significantly reduced, whereby the bumps are formed at low cost.
Conventionally, aluminum pads are subjected to a zincate treatment as a pretreatment for plating when forming the bumps by electroless plating. Specifically, a semiconductor wafer is immersed in a treatment solution including Zn ions, whereby the surface of the pads is replaced by Zn according to the reaction shown by 2Al+3Zn2+→2Al3++3Zn. The entire semiconductor wafer is then immersed in an electroless plating solution, thereby causing a plating metal to be deposited. The process may be rationalized by batch processing in which a plurality of semiconductor wafers is immersed in the plating solution.
The aluminum pads which become GND electrodes are electrically connected with an Si substrate of the semiconductor wafer. The Si substrate is electrically connected with the electroless plating solution. When electrons in the Si substrate are released into the electroless plating solution, the potential of the aluminum pads is changed. Since the amount of electrons used for a chemical reaction is decreased by such a grounding effect, ionic bonding rarely occurs, whereby replacement of the surface of the aluminum pads by Zn is insufficient in the zincate treatment. Moreover, the plating rate is changed by influence of the grounding effect, whereby deposition of the plating metal is affected.
There is a case where a resist is applied to a considerable thickness to the back side and a region near the periphery (from the periphery of the surface to the side) of the semiconductor wafer in order to prevent the influence of the grounding effect. The zincate treatment and the plating treatment are performed while preventing the electroless plating solution from coming in contact with a region near the periphery and the back side of the semiconductor wafer in this manner.
A resist is applied to the back side of the semiconductor wafer while chucking (adsorbing under vacuum) the side on which the bumps are formed (main surface of the semiconductor wafer) on a rotating table of a spin coater. In this case, the bump formation side must be prevented from being damaged so that the subsequent growth of plating is not affected.